In this dye diffusion transfer recording system, a heat-sensitive transfer sheet (hereinafter also referred to as an ink sheet) containing dyes is superposed on a heat-sensitive transfer image-receiving sheet (hereinafter also referred to as an image-receiving sheet), and then the ink sheet is heated by a thermal head whose exothermic action is controlled by electric signals, in order to transfer the dyes contained in the ink sheet to the image-receiving sheet, thereby recording an image information. Three colors: cyan, magenta, and yellow, are used for recording a color image by overlapping one color to other, thereby enabling transferring and recording a color image having continuous gradation for color densities.
In recent years, because an acceleration of a printer can shorten user's waiting time in the case where print is conducted in a photo shop for user's advantage, high-speed printers in the sublimation-type thermal transfer recording system, which can provide a print in a short time, have been developed and commercialized one after another.
In wide spread use of the printers in the sublimation-type thermal transfer recording system, there is a demand for a printer providing prints at good image quality under various environmental conditions without depending on an installation site. That is, in order to satisfy user's needs, it is necessary to provide a print good in image quality and free from image defect, not only under the standard air-conditioned environmental condition of offices and shops at a temperature of 23° C. to 27° C. and a humidity of 50% to 70%, but also, for example; under a high-temperature high-humidity condition in summer (e.g., temperature: 35° C., humidity: 80%) and a low-temperature low-humidity condition in winter (e.g., temperature: 10° C., humidity: 20%).
Recently, heat-sensitive transfer image-receiving sheets in which a receptor layer contains latex that is an aqueous dispersion of a thermoplastic resin have been proposed. That these image-receiving sheets provide excellent print properties including a proper sensitivity and absence of white spot (white spot by printing-failure in the solid image) is disclosed (see, e.g., JP-A-8-2123 (“JP-A” means unexamined published Japanese patent application), JP-A-2006-264092, JP-A-2007-160885 and JP-A-2006-88691). As a means for applying resistance to the white spot, there are disclosed a method in which a heat insulation layer, that is free of a resin having a poor resistance to an organic solvent, and a receptor layer are formed by the simultaneous multilayer coating (see, e.g., JP-A-2007-160885), and a method in which a heat insulation layer and a layer adjacent to the heat insulation layer on the receptor layer side are formed by the simultaneous multilayer coating (see, e.g., JP-A-2006-88691). Further, a method in which a heat insulation layer is formed by coating so that the heat insulation layer has a laminated structure including at least two layers is also proposed (see, e.g., JP-A-2006-62114).
However, these previous heat-sensitive transfer image-receiving sheets cause such a problem that even though an excellent image quality of print can be obtained under the standard conditions of, for example, temperature 25° C. and humidity 60%, the white spot at a low density portion remarkably arises under the conditions of low temperature and low humidity, for example, temperature 15° C. and humidity 20%. Further, they cause such a problem that uneven density owing to a transfer failure at a high density portion arises under the conditions of high temperature and high humidity. Accordingly, it has been earnestly desired to dissolve the aforementioned problems so that an excellent print can be provided under the various environmental conditions.